Hydrosilylation chemistry, typically involving a reaction between a silyl hydride and an unsaturated organic group, is the basis for synthetic routes to produce commercial silicone-based products like silicone surfactants, silicone fluids, silanes, as well as many addition cured products like sealants, adhesives, and silicone-based coating products. Typical hydrosilylation reactions use precious metal catalysts to catalyze the addition of a silyl-hydride (Si—H) to an unsaturated group, such as an olefin. In these reactions, the resulting product is a silyl-substituted, saturated compound. In most of these cases, the addition of the silyl group proceeds in an anti-Markovnikov manner, i.e., to the less substituted carbon atom of the unsaturated group. Most precious metal catalyzed hydrosilylations only work well with terminally unsaturated olefins, as internal unsaturations are generally non-reactive or only poorly reactive. There are currently only limited methods for the general hydrosilylation of olefins where after the addition of the Si—H group there still remains an unsaturation in the original substrate. This reaction, termed a dehydrogenative silylation, has potential uses in the synthesis of new silicone materials, such as silanes, silicone fluids, crosslinked silicone elastomers, and silylated or silicone-crosslinked organic polymers such as polyolefins, unsaturated polyesters, etc.
Various precious metal catalysts are known in the art. For example, U.S. Pat. No. 3,775,452 discloses a platinum complex containing unsaturated siloxanes as ligands. This type of catalyst is known as Karstedt's catalyst. Other exemplary platinum-based hydrosilylation catalysts that have been described in the literature include Ashby's catalyst as disclosed in U.S. Pat. No. 3,159,601, Lamoreaux's catalyst as disclosed in U.S. Pat. No. 3,220,972, and Speier's catalyst as disclosed in Speier, J. L.; Webster, J. A.; Barnes, G. H. J. Am. Chem. Soc. 1957, 79, 974.
There are examples of the use of Fe(CO)5 to promote limited hydrosilylations and dehydrogenative silylations. (See Nesmeyanov, A. N.; Freidlina, R. Kh.; Chukovskaya, E. C.; Petrova, R. G.; Belyaysky, A. B. Tetrahedron 1962, 17, 61 and Marciniec, B.; Majchrzak, M. Inorg. Chem. Commun. 2000, 3, 371). The use of Fe3(CO)12 was also found to exhibit dehydrogenative silylation in the reaction of Et3SiH and styrene. (Kakiuchi, F.; Tanaka, Y.; Chatani, N.; Murai, S. J. Organomet. Chem. 1993, 456, 45). Also, several cyclopentadiene iron complexes have been used to varying degrees of success, with the work of Nakazawa, et al showing interesting intramolecular dehydrogenative silylation/hydrogenation when used with 1,3-divinyldisiloxanes. (Naumov, R. N.; Itazaki, M.; Kamitani, M.; Nakazawa, H. J. Am. Chem. Soc. 2012, 134, 804).
A rhodium complex was found to give low to moderate yields of allyl-silanes and vinyl silanes. (Doyle, M. P.; Devora G. A.; Nevadov, A. O.; High, K. G. Organometallics, 1992, 11, 540). An iridium complex was also found to give vinyl silanes in good yields. (Falck, J. R.; Lu, B. J. Org. Chem. 2010, 75, 1701) Allyl silanes could be prepared in high yields using a rhodium complex (Mitsudo, T.; Watanabe, Y.; Hori, Y. Bull. Chem. Soc. Jpn. 1988, 61, 3011). Vinyl silanes could be prepared through the use of a rhodium catalyst (Murai, S.; Kakiuchi, F.; Nogami, K.; Chatani, N.; Seki, Y. Organometallics, 1993, 12, 4748). Dehydrogenative silylation was found to occur when iridium complexes were used (Oro, L. A.; Fernandez, M. J.; Esteruelas, M. A.; Jiminez, M. S. J. Mol. Catalysis 1986, 37, 151 and Oro, L. A.; Fernandez, M. J.; Esteruelas, M. A.; Jiminez, M. S. Organometallics, 1986, 5, 1519). Vinyl silanes could also be produced using ruthenium complexes (Murai, S.; Seki, Y.; Takeshita, K.; Kawamoto, K.; Sonoda, N. J. Org. Chem. 1986, 51, 3890).
A palladium-catalyzed silyl-Heck reaction was recently reported to result in the formation of allyl-silanes and vinyl silanes (McAtee, J. R.; Martin, S. E. S.; Ahneman, D. T.; Johnson, K. A.; Watson, D. A. Angew. Chem. Int. Ed. 2012, 51, 3663); McAtee, J. R.; Yap, G. P. A.; Watson, D. A. J. Am. Chem. Soc. 2014, 136, 10166).
U.S. Pat. No. 5,955,555 describes the synthesis of certain iron or cobalt pyridine di-imine (PDI) complexes bearing two ionic ligands. The preferred anions are chloride, bromide and tetrafluoroborate. U.S. Pat. No. 7,442,819 describes iron and cobalt complexes of certain tricyclic ligands containing a “pyridine” ring substituted with two imino groups. U.S. Pat. Nos. 6,461,994, 6,657,026, and 7,148,304 describe several catalyst systems containing certain transition metal-PDI complexes. U.S. Pat. No. 7,053,020 describes a catalyst system containing, inter alia, one or more bis(arylimino) pyridine iron or cobalt catalyst. Chink et al describe bis(arylimino) pyridine cobalt complexes with anionic ligands (Bowman, A. C.; Milsmann, C.; Bill, E.; Lobkovsky, E.; Weyhermüller, T.; Wieghardt, K.; Chink, P. J. Inorg. Chem. 2010, 49, 6110 and Bowman, A. C.; Milsmann, C.; Atienza, C. C. H.; Lobkovsky, E.; Wieghardt, K.; Chink, P. J. J. Am. Chem. Soc. 2010, 132, 1676.) U.S. Pat. Nos. 8,765,987, 8,895,770, and 8,927,674, and U.S. Patent Publication No. 2015/0137033 describe hydrosilylation and/or dehydrogenative silylation with cobalt, iron, or other first-row transition metal pyridine diimine complexes. The catalysts and catalyst systems disclosed in these references employ the use of a strong reducing agent, such as an alkyl lithium or alkali metal borohydride, to form precatalysts or generate active catalysts in situ. A particular deficiency of using strong reducing agents to activate base metal catalysts towards hydrosilylation or dehydrogenative silylation is the disproportionation of alkoxysilylhydrides to generate pyrophoric silane (SiH4). In general, the use of alkyl lithiums, Grignards, and alkali metals to activate catalysts is disadvantageous. U.S. Patent Publication No. 2014/0343311, WO 2013/043783 and WO 2013/043846 describe the use of a promoter to activate base metal compounds and complexes towards hydrosilylation without the need for a strong reducing agent.